1. Field of the Invention
The present invention is generally directed to the field of particulate material separating devices, and more particularly, to a computer controlled separator device for separating dry, granular, free-flowing material according to particle density.
2. Description of the Related Art
Conventional gravity separator devices use an inclined perforated separator deck, which is vibrated, in combination with an air flow directed vertically upwards through the separator deck in order to separate material into fractions or sections by weight. Typically, gravity separator devices are used to improve product quality in seed and grain, mineral, and recycling applications. The inlet end of the deck is elevated with respect to the outlet end to define an end raise. End raise is adjusted to control the rate at which material flows over the deck. A first side of the deck is elevated with respect to a second side to define a side tilt. Side tilt is adjusted to control the rate at which heavier material is conveyed up hill on the deck. By supplying vertically moving air, a lifting action is created that acts upon each particle in the bed of a product to be separated. The air flow also results in a vigorous washing effect whereby fine dust and dirt is removed from the product to be separated.
The separator deck is vibrated to provide an agitation and a conveying action. With each vibration stroke, the agitation action lifts the bed of material and throws it up into the air flow. In general, the air flow velocity is set at a value that is an average of that required to lift the bed of material. This value is lower than the terminal velocity of the particles so that, when lifted by the agitation action, all particles will fall back toward the deck surface against the air flow. The rate of fall is related to the weight of the particle and to the aerodynamic nature of the particle. Each individual particle varies from an average particle mass to some degree. In accordance with the degree of variance, heavier particles fall faster against the air flow and lighter particles fall slower against the air flow. When the bed of material has been subjected to a few lifting and falling cycles, stratified layers are generated, with the lightest material being on top of the bed and the most dense material collecting on the bottom of the bed. Intermediate particles having characteristics close to the average characteristics of the mass of the product are located in middle zones between the heaviest and lightest particles.
In addition to the agitation action, the vibration of the separator bed provides a conveying action. The conveying action imparts a thrust to the particles as they are lifted and thrown into the air. The deck surface retracts while the particles are in the air, and advances as the particles fall back to the deck surface. Heavier particles that are on the bottom of the bed are situated in closer contact with the deck surface, and are conveyed at a faster rate than lighter particles that are at the top of the bed. The deck surface is tilted in a direction opposite to the conveying action provided by the vibration. Lighter material that is on top of the bed is not affected as much by the conveying action, and tends to flow downhill in the direction of the side tilt.
With proper adjustment of air flow, separator bed vibration speed, and separator bed side tilt and end raise, a bed of material may be effectively separated. Denser particles on the bottom of the bed move uphill in one direction because of the vibrating conveying action. Lighter particles on the top of the bed flow downhill in an opposite direction because of the agitation action and side tilt. Intermediate particles move at a speed and in a direction that is directly related to the weight and aerodynamic qualities of the particles.
One technique for adjusting the end raise and side tilt in a gravity separator device is disclosed in U.S. Pat. No. 2,759,605 to Steele, wherein two screw jacks are used to accomplish these adjustments. A major disadvantage with this type of adjustment assembly is the need to release and secure clamps before and after adjustments are made. Another disadvantage is that the machine must be stopped in order to allow the operator to make any adjustments. This can be both time consuming and costly since any down-time takes away from productive separating time.
Another technique is shown in U.S. Pat. No. 5,024,334 to Misra et at., in which a detector detects the movement of control particles with respect to a gravity table in order to control a separation process. A disadvantage to this technique is that control particles must be added, thereby introducing unwanted impurities into the product to be separated.
In another device, shown in U.S. Pat. No. 4,563,271 to Schroder et at., a percussion jig has a carrier for material to be separated. In the discharge regulation system that supplies the separated materials to different outlets, a float generates a signal, which is used to control the discharge gate at the output.
U.S. Pat. No. 4,342,654 to Lambert discloses a separator having a liquid-filled tank with sensors to detect the level of separation of two layers in the bed of the separator. In response to the sensor signals, the system adjusts a solenoid valve to control the air venting process of the separator. U.S. Pat. No. 4,991,721 to Misra et at. shows sensing of the quantity of undersized material separated by a screen and of the quantity of oversized material separated by an air-lift to effect adjustments to the screen or air-lift.
Other prior art techniques, such as those described by U.S. Pat. No. 4,765,489 to Satake and 3,933,249 to Welsh et at., use light sensitive elements to monitor the product output from a product separator, and move a product recovering device in response to changes in product output.